Cash, Cash Equivalents, and Available-For-Sale Investments - Portfolio of Cash and Investments in Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	$ 197,959	$ 252,760
Cash, including restricted cash	37,614	26,947
Total cash and investments in marketable securities	262,026	302,194
Corporate Notes and Bonds [Member] | Fair Value Hierarchy Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	138,515	241,158
U.S. Corporate Commercial Paper [Member] | Fair Value Hierarchy Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	59,444	3,990
Obligations of U.S. Government Agencies [Member] | Fair Value Hierarchy Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments		6,108
Obligations of U.S. States and Municipalities [Member] | Fair Value Hierarchy Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments		1,504
Money Market Funds [Member] | Fair Value Hierarchy Level 1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Money market funds	$ 26,453	$ 22,487